1. Field of the Invention
This invention relates to a laser driving method and device for driving a light source of a laser beam for carrying out recording to and/or reproduction from a recording medium such as an optical disc, and a recording/reproducing device and method. Particularly, it relates to a laser driving method and device for driving a violet short-wavelength semiconductor laser such as a GaN-based or InGaN-based semiconductor laser, and a recording/reproducing device and method.
2. Description of the Related Art
Recently, there has been a significant progress in the technique for increasing the density of a recording medium. For example, in order to increase the density of an optical disc, it is basically conceivable to increase the numerical aperture (NA) of the optical system or shorten the wavelength of the light source.
When shortening the wavelength of the light source, if a semiconductor laser (laser diode (LD)) is used as the light source and the wavelength of its laser beam is shortened, a band gap necessary for semiconductor laser emission is increased and therefore the operating voltage of the semiconductor laser is increased (raised). Particularly, with a wavelength of approximately 400 nm as in a violet laser, the laser cannot be driven by a power-supply voltage of 5 V, which is generally used for a circuit power supply.
Meanwhile, in an equipment using such a violet semiconductor laser, increase in the power-supply voltage of the circuit causes increase in the power consumption and enormous increase in the calorific value, making it difficult to design the equipment. In the case of a short-wavelength semiconductor laser with a wavelength of approximately 400 nm, large variance in the operating current is observed from the beginning to the end of the operating life. Particularly, in the case of a GaN-based semiconductor laser, it is known that the operating current at the end of the life varies approximately 1.5 times greater than at the beginning. If a high circuit power-supply voltage is set in consideration of this aspect, the power consumption and the calorific value are increased further.
In view of the foregoing status of the art, it is an object of the present invention to provide a laser driving method and device and a recording/reproducing device and method which enable reduction in the power consumption and prevention of difficulty in the circuit design.